ALKYNES - Chapter 7

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ALKYNES - Chapter 7
nomenclature - (chapt 5), structure,
classification acidity of terminal acetylenes -
(chapt 4) alkylation prep - dehydrohalogenation
(-2HX) or double ?-elimination
reduction - H2/M (chapt 6) and
chemical hydroboration (chapt 6) - protonation
- oxidation (hydration) enol-keto
tautomerism addition of Hg, HX, X2, H2O (chapt
6) synthesis (chapts 6)
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blue - chemistry from previous chapters
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nomenclature - structure, classification acidity
of terminal acetylenes ) alkylation
?-elimination
reduction - H2/M chemical hydroboration -
protonation - oxidation
enol-keto tautomerism
addition Hg/H2O, HX, X2 synthesis
but first
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nomenclature - structure, classification acidity
of terminal acetylenes ) alkylation
?-elimination
reduction - H2/M chemical hydroboration -
protonation - oxidation
enol-keto tautomerism
addition Hg/H2O, HX, X2 synthesis
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acetylene, ethyne
Structure - two general types

(1) internal - R and R alkyl, Aryl, etc.
(2) terminal - R alkyl, Aryl, etc.
lt-- creates additional chemistry
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Alkyne Nomenclature
Common alkyl alkyl' acetylene
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Nomenclature
IUPAC - longest chain containing the most
important functional group(s) root -alkyne
4-chloro-6-cyclohexyl-5-methyl-2-hexyne
add substituents with s
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Acetylene - linear geometry - sp hybridization
180o bond angles
R-C-C-R
? -bond 180o bond angle
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Name ______________ seat ____
Write the product(s) of the following reactions.
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Acidity of organic compounds

pKa 25
H-Csp
Why ? recall chapter 4
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Relative basicity (acidity)
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Acid-Base reactions
organometallic reagent (15)
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Acid-Base reactions
last Thursday
R' alkyl D
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Alkylation of Acetylides
Recall RX type substitution
acetylide anions undergo substitution rx
with 1o alkyl halides
form new C-C bonds
termed alkylation
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Alkylation of Acetylides
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Alkylation of Acetylides
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Alkylation of Acetylides

• Acetylide anions - 2 and 3 halides
• ?-eliminates (strong base, reverse of addition)

no alkylation 2R-X
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Preparation Dehydrohalogenation (-2 HX)
two ?-eliminations
2 arrangements of diBrs gt same acetylene
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Preparation Dehydrohalogenation (-2 HX)
two ?-eliminations
2 arrangements of diBrs gt same acetylene
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Preparation Dehydrohalogenation (-2 HX)
two ?-eliminations
2 arrangements of diBrs gt same acetylene
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Preparation Dehydrohalogenation (-2 HX)
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Reactions - several like CC - additions
A. Reduction - addition of hydrogen
syn addition (2x)
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Reactions - several like CC - additions
A. Reduction - addition of hydrogen
With choice of catalyst - stop at olefin (add 1
eq H2).
Lindlar cat.
syn addition (2x)
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Chemical reduction of a triple bond.

trans olefin for internal acetylenes
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Acetylene chemistry - recall olefin chemistry
R H, alkyl
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Hydroboration of an internal alkyne
terminal
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Terminal acetylene
hindered borane adds once
di-sec-isoamylborane or HB(sia)2
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Terminal acetylene
hindered borane adds once
di-sec-isoamylborane or HB(sia)2
tautomerism H transfer (O to C)
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internal with oxidation - ketone
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regiochemistry
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enol-keto tautomerism H transfer C ? O
from HB/O Hg2/H2O other rxs
mechanism e(-) arrows
or
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Hydration of acetylenes
terminal yne - HBR2/O ? aldehyde
- Hg/H2O ? ketone
internal yne
- either ? ketone(s)
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electrophilic additions Br2 / Cl2
Assume bromonium (chloronium) ion ( like alkene
X2 addition )
Mechanism for 1st addition of X2
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addition of HX
vinyl bromide
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addition of HX - second addition
2o carbocation with resonance
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How could the vinyl bromide be converted into the
Z-olefin? Use any number of reactions but show
all necessary reagents and expected products of
each step.
how?
a. H2/Lindlar(cat.)
how?
Na-NH2
or b. (1)BH3, (2)AcOH/?
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convert 2-bromopropene to 2-hexanone
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compare carbon skeleton functional groups
convert 2-bromopropene to 2-hexanone
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compare carbon skeleton functional groups
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